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    <meta charset="UTF-8">
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    <title>Document</title>
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<script>
    function getrun_feb_days() {
        var year = prompt("请输入年份：")
        if (isRunYear(year)) {
            alert('今年是闰年，有29天。')
        }else{
            alert('今年是平年，有28天。')
        }
    }
    getrun_feb_days()
    console.log(Math.PI);

    function isRunYear(year) {
        var flag = false
        if (year & 4 == 0 && year % 100 != 0 || year % 400 == 0) {
            flag = true
        }
        return flag
    }
</script>
</html>